The National Synchrotron Light Source (NSLS) at Brookhaven National Laboratory (BNL) is a user facility devoted to research that uses infrared, visible, ultraviolet, and X-radiation. Four beamlines are used regularly for macromolecular and virus x-ray crystallography (abbreviated "PX" in this document), and five more are in various stages of development. The requests for time on these beamlines are appreciably greater than the time available. Typically, prospective users will wait six to nine months for access. This Research Resource will enhance the capabilities of the NSLS in PX through innovative research and development programs, in which we will push the state of the art in beamline software and modern detector systems for PX. We will provide infrastructure and core support for the upgrading of three of the existing beamlines to speed up data collection and on-site data reduction, and will assist in development of PX programs on two additional beamlines. A major goal is to make the NSLS a center for structural biology in the northeastern United States. The resource represents an extension of the close cooperation that exists between the BNL Biology Department and the NSLS.